The standard team of the third generation partnership project (3GPP) is currently focused on studying the evolution of Packet Switched Core (PS Core) and Universal Mobile Telecommunication System Radio Access Network (UTRAN), in order to enable the Evolved Packet Switched Core (EPC) to provide high transmission rate and low transmission delay, and support the Evolved UTRAN (E-UTRAN), UTRAN and GSM EDGE Radio Access Network (GERAN), as well as accessing and mobility management of many radio technologies, such as Global System for Mobile communications (GSM) and Enhanced Data Rate for GSM Evolution (EDGE) and the like. This evolved mobile communication system is called Evolved Packet System (EPS).
FIG. 1 shows a diagram of network architecture in the GSM/Universal Mobile Telecommunications System (UMTS) and EPS network related to the disclosure in the prior art, as shown in FIG. 1, comprising:
a mobile station 101, which is called Mobile Station (MS) or User Equipment (UE). A terminal with a capacity of accessing two kinds of radio networks is called a dual-mode terminal, while a terminal with a capacity of accessing multiple kinds of radio networks is called multi-mode terminal. Therefore, MS/UE is a dual-mode or multi-mode terminal that can access GSM/UMTS network and EPS network, which is uniformly represented by UE or terminal below.
E-UTRAN 102: the radio access network of the evolved EPS network may provide a high uplink/downlink rate, low transmission delay, and reliable radio transmission. A network element included in the E-UTRAN is an Evolved NodeB (eNodeB) that provides radio resources for the access of the terminal.
Mobility Management entity (MME) 103 is a control plane entity as well as a server for temporarily saving user data, which is responsible for managing and saving a UE context, such as UE/subscriber identity, mobility management state, user security parameters, for distributing a temporary identity for a subscriber, and for authenticating the subscriber when the UE resides in the tracking area or the network. MME is mainly responsible for access control, mobility management and other tasks when the UE accessing from E-UTRAN.
GERAN/UTRAN 104: a radio access network of traditional GSM/UMTS.
GSM/UMTS network is divided into Circuit Switching (CS) domain and Packet Switching (PS) domain.
General Packet Radio Service (GPRS) Serving GPRS Support Node (SGSN) 105: GPRS SGSN is a control network element in PS domain of the GSM/UMTS network with a main function of recording the location information of the UE and performing transmission and reception of mobile packet data between the UE and the Gateway GPRS Supporting Node (GGSN). SGSN is mainly responsible for access control, is mobility management and other tasks when the UE is accessing from PS domain of the GSM/UMTS network.
Mobile Switching Center (MSC)/Visitor Location Register (VLR) 106: the MSC/VLR may also be a new function entity MSC Server after 3GPP Release (R) 4 stage, which is uniformly represented by MSC/VLR in the disclosure. The MSC/VLR is the network element of core network in CS domain of the GSM/UMTS network, responsible for control of subscriber accessing, mobility, voice and SMS service in circuit domain.
Serving Gateway (S-GW) and Packet Data Network Gateway (P-GW) 107: S-GW is a user plane entity, which is responsible for user plane data routing processing; P-GW is responsible for gateway function on accessing to Packet Data Network (PDN) by user. P-GW and S-GW may be arranged jointly in a physical entity or separately in different physical entities.
Operator Internet Protocol (IP) network means a network in which an operator provides services. An example of IP network is an IP Multimedia Core Network Subsystem (IMS), which is just a kind of operator IP network. IMS is a Session Initiation Protocol (SIP)-based network architecture proposed by 3GPP which constructs an open and flexible service environment, supports multimedia applications, and provides rich multimedia services to users.
In a 3GPP mobile communication system, when a terminal is in idle state, the terminal and a network element of core network run a timer respectively in order to guarantee the network to page the terminal and waste no network resource in the case that the terminal is inaccessible, wherein the timer in the terminal is called periodic update timer, and the timer in the network element of core network is called implicit detach timer. When the periodic update timer of the terminal expires, a periodic update will be initiated, and then the terminal and the network element of core network restart their own timers. Generally, the implicit detach timer of the network element of core network has longer time than that of the periodic update timer of the terminal. Thus, if the implicit detach timer of the network element of core network expires while no update message is received from the terminal, it would be known that the user is out of coverage is area at present, and the terminal is inaccessible, then it will waste air interface resources for paging this terminal later. At this point, the network element of core network sets the user in the implicit detach state. This mechanism is to ensure that the user is accessible.
The terminal respectively has independent periodic update timers for the circuit domain of the GSM/UMTS network, the packet domain of the GSM/UMTS network and the EPS network: periodic Location Area Update (LAU) timer for the circuit domain of the GSM/UMTS network, periodic Routing Area Update (RAU) timer for the packet domain of the GSM/UMTS network, and periodic Tracking Area Update (TAU) timer for the EPS network. The network elements of core network MSC/VLR, SGSN and MME also respectively run three implicit detach timers.
In a GSM/UMTS network, the UE may perform CS and PS attach/update respectively. When performing CS and PS attach/update respectively, the UE sends LAU and RAU request message to the GERAN/UTRAN respectively. The MSC/VLR receives the LAU request message through the GERAN/UTRAN and performs the update/attach process of the CS domain. SGSN receives the RAU request message through the GERAN/UTRAN and performs the update/attach process of the PS domain. As the respective mode in which the CS domain and the PS domain perform attach/update needs to respectively occupy radio resources and perform signaling exchange, Therefore a Gs interface is introduced between the MSC/VLR and the SGSN.
When the Gs interface is introduced, in consideration of compatibility and flexibility of network deployment, network modes I, II and III are introduced. When the network works in mode I, the UE performs update through combined RAU/LAU process. A Gs association exists between the MSC/VLR and the SGSN. When the network works in mode II/III, the UE performs RAU and LAU processes respectively.
In order to perform CS services such as call and SMS and the like when the UE is accessed from E-UTRAN, an SGs interface is also introduced between the MME and the MSC/VLR.
At the same moment, the user has only one Gs association or one SGs association is in the MSC/VLR.
Gs association is established through the combined attach or combined routing area/location area update, while the SGs association is established through the combined attach or combined tracking area/location area update. In the combined attach or combined routing area/location area update, or in the combined attach or combined tracking area/location area update, the UE performs attach or update in the SGSN/MME firstly, then the SGSN/MME initiates CS attachment or update to the MSC/VLR according to the type of attach/update, and establishes the Gs/SGs association to the MSC/VLR. The flow is shown in FIG. 2.
FIG. 2 shows an interaction flow chart of establishing Gs/SGs interfaces according to the prior art. As shown in FIG. 2, it comprises steps from S202 to S208 as follows:
S202: UE sends a combined register/combined update request message to the SGSN/MME.
S204: The SGSN/MME sends a CS register request message to MSC/VLR.
S206: The MSC/VLR sends a CS register response message to the SGSN/MME.
S208: The SGSN/MME sends a combined register/combined update response message to the UE, the SGSN/MME and the MSC/VLR establishes Gs/SGs interface.
Afterwards, after the UE moves, the UE will initiate a routing area update or tracking area update to notify the current location information to the SGSN/MME. If the Location Area Identity (LAI) of the user also changes, then the UE initiates a combined routing area/location area update or combined tracking area/location area update, and the SGSN/MME further updates the MSC to ensure that the LAI of the user in the MSC is accurate. After the Gs/SGs association is established, the periodic LAU timers of the CS in the MSC/VLR and the terminal are deactivated, and the accessibility of the terminal user is guaranteed by the packet domain periodic RAU/TAU timer. Therefore, the terminal needs not to perform periodic location area update.
At the early stage of E-UTRAN deployment, an area covered by both GERAN/UTRAN and E-UTRAN exists. When the user resides in the area covered by both GERAN/UTRAN and E-UTRAN, in order to reduce excessive air-interface signaling caused by repeatedly selecting a network between GERAN/UTRAN and E-UTRAN and is initiating a registration by the user, 3GPP defines Idle mode Signaling Reduction (ISR). In ISR, the main idea is that when the UE registers with both SGSN and MME, both SGSN and MME save user context information, and the UE also saves the, registration information of the two networks, such that no TAU and RAU process needs to be performed when the UE subsequently selects between the two networks unless the current routing area or the current tracking area list of the UE is not registered. In the case of ISR, as the user does not initiate an update when changes the access system, therefore the core network does not know which access system the UE resides when the user is in idle state. At this point, it needs page in both SGSN and MME when paging a user. When ISR is activated, MME and SGSN save address information for each other, such that, the MME or SGSN may find each other and initiate paging when the MSC/VLR pages the user.
FIG. 3 shows an interaction flow chart comprising SGs activation and MME receiving paging from the MSC/VLR according to the prior art. As shown in FIG. 3, the interaction flow chart comprising ISR activation, SGs activation between MSC/VLR and MME, and MME receiving paging from the MSC/VLR comprises steps from S302 to S310 as follows:
S302: The MSC/VLR initiates paging to the MME through the SGs interface.
S304: The MME, according to the location information of the user and through eNodeB where the UE is located, initiates CS paging to the UE.
S306: As ISR has been activated and the UE user is in idle state, the MME forwards the paging message from the MSC/VLR to the SGSN according to the location information of the SGSN saved in the MME.
S308: The SGSN, according to the location information of the terminal user thereof and the location information in the paging message, through the GERAN/UTRAN where the UE is located, initiates CS paging to the UE.
S310: The UE performs fallback or cell reselection and the like according to the prior art to return a paging response from the CS domain of GSM/UMTS network.
For ISR-activated UE, when the UE is in idle state, it is necessary to maintain the periodic TAU and periodic RAU timers respectively. When the periodic TAU timer of the UE expires, if the UE currently resides in the Long-Term Evolution (LTE), the UE will initiate a periodic TAU; if the UE does not reside in the LTE currently, the UE will not be triggered to initiate the periodic TAU. At this point, the UE needs to remember to further initiate a periodic TAU when returning to the area covered by LTE. The processing on expiration of the periodic RAU timer of the UE is similar to that on the expiration of the periodic TAU timer.
Based on above background, the following scene is considered. UE registers in the GSM/UMTS network firstly, then registers in the EPS network; after completion of the above registrations, an SGs interface is established and activated between the MME and the MSC/VLR; further, an ISR association is established between the MME and the SGSN; the UE registers in the SGSN, MME and MSC/VLR saves the registration information in these networks, and identifies that ISR has been activated. When the UE moves into the GSM/UMTS network and the current routing area has been registered, as ISR has been activated, the UE will not initiate a RAU process; the current routing area of the UE is identified through Routing Area Identity (RAI). At this point, the SGs interface between the MME and the MSC/VLR still exists, and the implicit detach timer in the MME still runs. After the E-UTRAN periodic TAU timer in the terminal expires, as the UE resides in the GSM/UMTS network, the UE will not initiate a periodic TAU to the MME. In this way, after a period of time, the MME may implicitly detach the terminal as the implicit detach timer expires and send a detach indication message to the MSC/VLR to deactivate the SGs interface. If MSC/VLR receives the detach indication message and believes that the user is still accessible and thereby initiates an implicit detach timer therein, then if the GSM/UMTS network works in the network mode I, the SGSN will not send an update to the MSC/VLR as it is impossible to activate the Gs interface between the MSC/VLR and the SGSN, and the periodic RAU process initiated by the UE is not a combined update; if the GSM/UMTS network works in the network mode II or III, the UE cannot know that a periodic LAU is needed to be initiated as the periodic LAU timer has been closed. Subsequently, when the implicit detach timer in the MSC/VLR expires, the MSC/VLR will think that the user is inaccessible and then identify the terminal as implicit detach. If the MSC/VLR thinks that the user is inaccessible when receives the is detach indication message from the MME, it will directly identify the terminal as implicit detach. No matter which of the above cases causes the MSC/VLR to identity the terminal as implicit detach, it will result in that the UE, although actually in an accessible network, cannot receive a call or SMS and the like as a called user.
Till now, the prior art has not proposed a solution to the above problem so as to ensure user accessibility.